'Why did my son die?': Mother Debra's never-ending nightmare

August 13 will be a date forever etched into the memory of Wagga woman Debra Plum.

On that day her worst nightmare began.

It hasn't stopped.

But today will bring Mrs Plum a chance to get the answers to the questions she so desperately craves – “why did my son die?”

A coronial inquest into the death of her son Jason Lee Plum, who committed suicide in the back of a police vehicle last year, begins today.

Mr Plum, 37, killed himself while in police custody just after 9pm on Saturday, August 13, The Daily Advertiserreports.

He had been arrested after police were called to the scene of a domestic dispute in Wagga's CBD.

Despite efforts of police to perform CPR, the avid rugby league player and kick boxer died the following day.

The incident sparked two investigations with an internal police investigation carried out by Griffith detectives running parallel to a coronial inquest.

After more than a year of nightmares and finding it hard to get out of bed every day, Mrs Plum and Mr Plum's stepfather, Trevor Marks, will face the three-day inquest in the hope it brings clarity and transparency to what happened that night.

“What I'm hoping is that the truth will come out about the events of that night,” Mrs Plum said.

“We want the truth to come out so people know and so maybe things can be changed so it doesn't ever happen again.”

A letter sent by Mrs Plum's lawyer to the coroner lists 26 questions she hopes will be answered.

It questions whether police followed protocols during Mr Plum's arrest, including searching his person and handcuffing.

It also raises questions in regards to a police database and information available on Mr Plum's criminal and psychological history.

While the couple's attention is on finding answers into his death, they are also firmly focused on ensuring a situation of this nature is the last of its kind.

“At the end of the night it was only Jason who died, but it could have been a lot worse,” Mr Marks said.

“It could have been a police officer who lost their life.”

While emotional, Mrs Plum said she was prepared to see the inquest through.

“It's been extremely hard the last few days. It never leaves you,” she said.